1. Field of the Invention
This invention relates to valve actuators, and particularly to a valve actuator for automatically closing or opening, upon the sensing of a predetermined condition, a valve having a rotatable closure member such as a butterfly, plug or ball valve.
2. Description of the Prior Art
Many industrial applications for rotary valves such as butterfly, plug and ball valves require a fail-safe mechanism that will automatically close or open a valve upon the occurrence of a predetermined condition. For example, in the petroleum industry it is often desirable to have valves that will automatically close and prevent the flow of petroleum upon the occurrence of a fire. Such valves are generally referred to as fail-close valves. Similarly, it may be desirable, upon the occurrence of a fire, to effect the automatic opening of a valve that controls the flow of water in a sprinkler system. Such a valve is generally known as a fail-open valve. A shortcoming associated with known rotary valve actuators having a fail-safe feature is that they typically provide the valve with only two states, i.e., either open or closed. Many times, however, it is desirable to operate a valve manually to an intermediate state so that the flow of the fluid through the valve may be controlled.
Another shortcoming associated with many known fail-safe actuators for rotary valves is that they can operate only in the fail-open mode or only in the fail close mode, but not both.
It is an object of this invention to provide a fail-safe actuator for a rotary valve that can automatically open or close the valve upon the sensing of a predetermined condition.
It is another object of this invention to provide a fail-safe actuator having the above characteristics that can effect the manual operation of the valve to any position intermediate the open and closed position in addition to the open and closed position.
It is a further object of this invention to provide a fail-safe actuator having the above characteristics that is a fully enclosed, self-energized actuating device and that is compact in construction and easy to operate.